Some sources claim 16 hp from factory stamped rockers to 1.6 RR on undercammed underheaded mild 350 engines...
But I think is a bit high too
On a well developed cam/head/exaust engine increased lift and valve acceleration from bigger ratio rocker can offset any possible gain, mainly on exaust due to increased valvetrain instability and too much overlap area to the engine.
Just my $.02
I'm just another Gearhead with a tool box, learning and helping.